1. Field of the Invention
The present invention generally relates to an inkjet head inspection device and, in particular, to the inkjet head inspection device that inspects for ink jet malfunctions in an inkjet head.
2. Description of the Related Art
Diverse types of printer heads are used for printers; e.g., an inkjet head is known in which a piezoelectric element presses a pressure chamber to eject ink existing in the pressure chamber from a nozzle.
To eject ink droplets from the inkjet head, an external driving power supply applies an electric signal to an individual electrode and a common electrode, which distorts the piezoelectric element. The distortion of the piezoelectric element changes the volume of the pressure chamber via a vibrating plate and increases the pressure exerted on the ink filled in the pressure chamber. By this increased pressure, the ink is ejected from the nozzle as ink droplets.
The number of nozzles of an inkjet head tends to multiply as print media become larger and with faster printing. With the multiplication of the nozzles, the number of nozzles to experience an ink jet malfunction increases.
The ink jet malfunction takes place mainly because of piezoelectric element failure or air bubbles intruded into the pressure chamber, the bubbles impeding transmission of the displacement of the piezoelectric element to the pressure chamber. The piezoelectric element failure includes its electrical connection fault as well as its physical fault. When an ink cartridge is replaced, air is liable to enter an ink passage and the entered air stays as bubbles in the pressure chamber, which is liable to cause an inkjet malfunction of a nozzle.
Since lack of ink ejection degrades print quality, it is needed to detect ink jet malfunctions.
In Japanese Published Unexamined Patent Application No. Hei 11-64175, a technique for detecting ink jet malfunctions is described. In this technique, an impedance analyzer is connected to each piezoelectric element per nozzle to measure its proper frequency and a piezoelectric element that vibrates at a different frequency from the proper frequency in its normal contact state is judged to be a faulty contact.
In Japanese Published Unexamined Patent Application No. 2000-318183, a relevant technique is described. This technique acquires a profile of a piezoelectric element's resonance point and electrically detects the state of ink charged in a recording head in order to prevent air bubble intrusion into the ink passage, which is caused on account of insufficiently charged ink in the recording head.
In Japanese Published Unexamined Patent Application No. 2000-355100, a nozzle inspection technique is described. This technique applies a voltage with a predetermined frequency to a piezoelectric element, as an input for measurement, to inspect for an ink jet malfunction due to air bubble intrusion, a clogged nozzle, etc. Based on the thus input voltage and an output voltage measured on the piezoelectric element after being driven, a phase lag and the measured value of output voltage are compared with prepared reference data.
In Japanese Published Unexamined Patent Application No. 2004-9501, a technique for detecting a piezoelectric element failure occurring or air bubble intrusion into the pressure chamber is described. This technique measures a piezoelectric element's resonance frequency when being driven and compares the thus measured resonance frequency with a reference resonance frequency data to determine a change in the resonance frequency.
However, the technique described in Japanese Published Unexamined Patent Application No. Hei 11-64175 has a problem in which its implementation requires a very complex structure including impedance analyzers connected to each piezoelectric element per nozzle and a cost increase. To implement the techniques described in Japanese Published Unexamined Patent Application Nos. 2000-318183, 2000-355100 and 2004-9501, it is inevitable to perform complex processing, which poses a problem that restraining cost is impossible.